索赔计数相依风险模型

考虑了一类索赔计数相依的风险模型,该模型假设每次主索赔可随机产生一副索赔,得到了该风险模型生存概率所满足的微积分方程,并在索赔额为指数分布的情形下,给出了生存概率的精确表达式.     

Validation of a regional Indonesian Seas model based on a comparison between model and INSTANT transports

The International Nusantara Stratification and Transport (INSTANT) program measured currents through multiple Indonesian Seas passages simultaneously over a three-year period (from January 2004 to December 2006). The Indonesian Seas region has presented numerous challenges for numerical modelers — the Indonesian Throughflow (ITF) must pass over shallow sills, into deep basins, and through narrow constrictions on its way from the Pacific to the Indian Ocean. As an important region in the global climate puzzle, a number of models have been used to try and best simulate this throughflow. In an attempt to validate our model, we present a comparison between the transports calculated from our model and those calculated from the INSTANT in situ measurements at five passages within the Indonesian Seas (Labani Channel, Lifamatola Passage, Lombok Strait, Ombai Strait, and Timor Passage). Our Princeton Ocean Model (POM) based regional Indonesian Seas model was originally developed to analyze the influence of bottom topography on the temperature and salinity distributions in the Indonesian seas region, to disclose the path of the South Pacific Water from the continuation of the New Guinea Coastal Current entering the region of interest up to the Lifamatola Passage, and to assess the role of the pressure head in driving the ITF and in determining its total transport. Previous studies found that this model reasonably represents the general long-term flow (seasons) through this region. The INSTANT transports were compared to the results of this regional model over multiple timescales. Overall trends are somewhat represented but changes on timescales shorter than seasonal (three months) and longer than annual were not considered in our model. Normal velocities through each passage during every season are plotted. Daily volume transports and transport-weighted temperature and salinity are plotted and seasonal averages are tabulated.     

Kaimal's isopleths from a closure model

Kaimal's isopleths for the spectra of the Kansas experiment are derived from a closure model built after Claussen's mechanisms for the spectral transfer of kinetic energy in a steady-state and horizontally homogeneous flow. The connection of the predicted three-dimensional spectrum with the measured one-dimensional one is accomplished via the additional assumption that turbulence in the Kansas experiment was basically isotropic.Partially financed by CAPES, FINEP and CNPq.On leave from Faculdade de Engenharia de Joinville, SC, Brazil.     

Validating the Runoff from the PRECIS Model Using a Large-Scale Routing Model

The streamflow over the Yellow River basin is simulated using the PRECIS （Providing REgional Climates for Impacts Studies） regional climate model driven by 15-year （1979-1993） ECMWF reanalysis data as the initial and lateral boundary conditions and an off-line large-scale routing model （LRM）. The LRM uses physical catchment and river channel information and allows streamflow to be predicted for large continental rivers with a 1°×1° spatial resolution. The results show that the PRECIS model can reproduce the general southeast to northwest gradient distribution of the precipitation over the Yellow River basin, The PRECIS- LRM model combination has the capability to simulate the seasonal and annual streamflow over the Yellow River basin. The simulated streamflow is generally coincident with the naturalized streamflow both in timing and in magnitude.     

Implementation of a one-dimensional enthalpy sea-ice model in a simple pycnocline prediction model for sea-ice data assimilation studies

To further explore enthalpy-based sea-ice assimilation, a one-dimensional(1D) enthalpy sea-ice model is implemented into a simple pycnocline prediction model. The 1D enthalpy sea-ice model includes the physical processes such as brine expulsion, flushing, and salt diffusion. After being coupled with the atmosphere and ocean components, the enthalpy sea-ice model can be integrated stably and serves as an important modulator of model variability. Results from a twin experiment show that the sea-ice data assimilation in the enthalpy space can produce smaller root-mean-square errors of model variables than the traditional scheme that assimilates the observations of ice concentration, especially for slow-varying states. This study provides some insights into the improvement of sea-ice data assimilation in a coupled general circulation model.     

An investigation of the sensitivity of a land surface model to climate change using a reduced form model

 In an illustration of a model evaluation methodology, a multivariate reduced form model is developed to evaluate the sensitivity of a land surface model to changes in atmospheric forcing. The reduced form model is constructed in terms of a set of ten integrative response metrics, including the timing of spring snow melt, sensible and latent heat fluxes in summer, and soil temperature. The responses are evaluated as a function of a selected set of six atmospheric forcing perturbations which are varied simultaneously, and hence each may be thought of as a six-dimensional response surface. The sensitivities of the land surface model are interdependent and in some cases illustrate a physically plausible feedback process. The important predictors of land surface response in a changing climate are the atmospheric temperature and downwelling longwave radiation. Scenarios characterized by warming and drying produce a large relative response compared to warm, moist scenarios. The insensitivity of the model to increases in precipitation and atmospheric humidity is expected to change in applications to coupled models, since these parameters are also strongly implicated, through the representation of clouds, in the simulation of both longwave and shortwave radiation. Received: 27 March 2000 / Accepted: 11 September 2000     

Fluctuation dissipation in a general circulation model

This paper considers the climate response to step function changes in the solar constant in two versions of a general circulation model with simplified geography. The NCAR CCM0 model is applied to an all-land planet with no topography (Terra Blanda). In one version there is moisture in the air (as well as self-generated clouds) as evaporated from an ideal surface at a fixed 80% of saturation. In the other version there is no moisture in the atmosphere. We examine the decay of natural anomalies in the large-scale temperature field in each model and compare the time dependence of the ensemble average with the average temporal behavior of the response to step function changes in the solar constant. The fluctuation-dissipation theorem of statistical mechanics makes specific predictions about the relationship between the two curves. We conduct the experiments for both versions of the model since the sensitivity is quite different for each. The theorem is found to hold reasonably well in each case.     

Surface energy budget model of a cave

Summary A simple surface energy budget model is developed and validated for an aboriginal rock art site in Western Australia. The thermal regime of the rock face is strongly dependent on the sky view factor for a vertical surface element and the sensible and latent heat fluxes are shown to be relatively unimportant. Using climatological data, the model is extended to form the basis for appropriate environmental management and conservation of the rock art.

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Zusammenfassung Es wird ein einfaches Oberflächenenergiebilanzmodell für eine Höhle mit Felszeichnungen der Eingeborenen in Westaustralien entwickelt und überprüft. Das thermische Regime der Felsoberfläche wird vom Bildwinkel des Himmels für ein vertikales Oberflächenelement dominiert, während sich die Flüsse fühlbarer und latenter Wärme als unbedeutend erwiesen. Die Berücksichtigung von klimatologischen Daten ermöglicht es, damit die Grundlagen für geeignete Umweltund Konservierungsmaßnahmen für das Kunstwerk zu schaffen.

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With 4 Figures     

Turbulent flow in a model plant canopy

An array of slender, vertical, cylindrical rods was used in a wind tunnel to simulate a plant canopy. Turbulence measurements were made with a cross hot wire, both inside and above the canopy. Measurements were also made inside the canopy when its top was covered by boards, leaving no space above the rods. This artificially confined canopy provided reference data.The results show an exponential wind profile and constant turbulence intensity, skewness and mixing length along the height of the (unconfined) canopy, the contribution of the eddies shed by the rods to the turbulence observed inside the canopy was small, but clearly apparent.     

Parameter sensitivity of a coupled atmosphere-ocean model

 The sensitivity of a coupled model to the oceanic vertical diffusion coefficient κ _v is examined. This is compared to the sensitivity of an ocean-only model forced by mixed boundary conditions (BC). The atmospheric component of the coupled model is a moist energy balance model. The ocean component is a 12-level geostrophic model, defined on a midlatitude β-plane. Atmosphere and ocean are coupled through the fluxes of heat and moisture at their interface. The coupled model contains a number of feedback processes which are not represented in the ocean-only model. This results in a temperature and salinity response to κ _v which is stronger in the coupled model than in the ocean-only model. On the other hand, there is a weaker response in oceanic processes such as meridional heat transport, deep-water formation at high latitudes, etc. Ocean-only sensitivity experiments were also performed with modified BCs, which parametrise the feedback processes included in the coupled model. These are the modified thermal BC of Rahmstorf and Willebrand and a modified freshwater BC proposed in the present study. Large-scale features of the response in oceanic surface fields are well represented with modified BCs. However, the sensitivity of the deep ocean temperature is only partly captured due to local differences in the surface response. The scaling behavior of the zonal overturning stream function was found to depend on the surface BCs. In contrast to this, the meridional overturning stream function basically scales with κ^0.5 _v in all sensitivity experiments. Differences in the heat transport response among the experiments are thus primarily related to differences in the temperature response. Received: 28 February 1997/Accepted: 12 September 1997     

Development of a hurricane boundary-layer wind model

Summary Hurricanes cause a variety of damage due to high winds, heavy rains, and storm surges. This study focuses on hurricanes’ high winds. The most devastating effects of sustained high winds occur in the first few hours of landfall. During the short period, hurricanes’ rainfall often increases, while the low-level pressure gradients continue to weaken. Latent heating does not appear to strengthen the surface winds. The indicator is that dry mechanisms such as the boundary layer processes and terrain are responsible for the damaging winds in the coastal areas. In this study, the design of a dry hurricane boundary layer wind model is described. The goal is to develop a forecast tool with near-real time applications in expeditious wind damage assessment and disaster mitigation during a hurricane landfall event. Different surface roughness lengths and topographic features ranging from flat land to the mountainous terrain of Taiwan were used in the model simulation experiments to reveal how the coastal environment affected the hurricane surface winds. The model performed quite well in all cases. The experiments suggested that the downward transfer of high momentum aloft played a significant role in the maintenance of high wind speeds at the surface. The surface wind maximums were observed on the lee sides of high terrain. The surface streamline analyses showed that the high mountains tended to block the relatively weak flow and caused small eddies, while they forced the stronger flow to turn around the mountains. Due to great difficulty in data collection, the hurricane boundary layer over land remains one of the least understood parts of the system. The dry model proves to be an effective way to study many aspects of hurricane boundary layer winds over a wide range of terrain features and landfall sites. The model runs efficiently and can be run on a medium-size personal computer. Received March 16, 2001 Revised September 10, 2001     

Adjoint of a parameterized moisture convection model

Summary Adjoint models have found use as dynamical tracers, helping to track a feature or phenomenon back to its origin. Their application to the study of atmospheric convection, however, is challenged by the complexity and nonlinearity of diabatic processes. Herein, the adjoint of a significantly simpler parameterized moisture (PM) model is described and tested. The PM model eliminates explicit moisture by making latent heating conditionally proportional to updraft velocity and providing a lower tropospheric heat sink mimicking rainwater evaporation.The PM adjoint, of course, is useful only if the parameterization can produce realistic results. Earlier work suggested that the PM framework possessed a fundamental flaw that made its storms have an excessive impact on their upstream environments. In fact, the adjoint was used to identify the origin of the discrepancies between PM and traditional cloud model storms, thereby leading to the parameterization improvements and dynamical insights recently discussed in Fovell (2002). The present paper is a companion to that study, describing how the adjoint model was constructed, tested and utilized. In addition, an even more realistic adjoint framework is described.     

Representing glaciers in a regional climate model

A glacier parameterization scheme has been developed and implemented into the regional climate model REMO. The new scheme interactively simulates the mass balance as well as changes of the areal extent of glaciers on a subgrid scale. The temporal evolution and the general magnitude of the simulated glacier mass balance in the European Alps are in good accordance with observations for the period 1958–1980, but the strong mass loss towards the end of the twentieth century is systematically underestimated. The simulated decrease of glacier area in the Alps between 1958 and 2003 ranges from −17.1 to −23.6%. The results indicate that observed glacier mass balances can be approximately reproduced within a regional climate model based on simplified concepts of glacier-climate interaction. However, realistic results can only be achieved by explicitly accounting for the subgrid variability of atmospheric parameters within a climate model grid box.     

Incorporating a semi-stochastic model of ocean-modulated westerly wind bursts into an ENSO prediction model

Prediction models of the El Niño-Southern Oscillation (ENSO) phenomenon often represent westerly wind bursts (WWBs), a significant player in ENSO dynamics, as stochastic forcing. A recent paper developed an observationally motivated semi-stochastic statistical model that quantifies the dependence of WWBs on large-scale sea-surface temperature. This WWB model is added here to a hybrid coupled model, thus activating a two-way SST-WWB feedback. The WWB model represents both the deterministic and stochastic elements of WWBs and thus is especially appropriate for ensemble ENSO prediction experiments. An ensemble of retrospective forecasts is performed for the years 1979–2002. Overall statistical measures of predictability are neither degraded nor improved relative to the hybrid, coupled general circulation model, perhaps because of the limitations of the hybrid coupled model and the initialization procedure used. While the present work is meant as a proof-of-concept, it is found that the addition of the WWB model does improve the prediction of the onset and the development of the large 1997 warm event, pointing to the potential for ENSO prediction skill improvement using this approach.     

Preliminary results From a partial LRTAP model based on an existing meteorological forecast model

Abstract

An existing state‐of‐the‐art regional meteorological model is coupled through appropriate constituent mass conservation equations to model the long‐range transport of atmospheric pollutants (LRTAP) under restrictive constraints on atmospheric chemistry and deposition. Particular emphasis is given to the importance of a good representation of turbulence and other sub grid‐scale processes in the planetary boundary layer (PBL), both in the formulation and in the interpretation of the results. The regional meteorological model provides not only forecasts of wind velocity and temperature, but also vertical diffusion profiles consistent with the evolution of its PBL. The transport in the LRTAP model is handled by computationally stable algorithms such that the time step may be chosen on the basis of accuracy rather than stability, and the chemistry is described by a simple four‐species model of the oxidation of sulphur dioxide and nitrogen dioxide. Results are presented of a sample 48‐h summer simulation over central and eastern North America, using real meteorological data and time‐averaged emission inventory data; parameters of the integration include a one‐hour time step, a horizontal resolution of 100 km and 15 variably spaced vertical levels, 10 of which are contained in the lower one third of the atmosphere. It is argued that despite the simplicity of the chemistry, the results are qualitatively realistic and the high impact of the PBL processes on LRTAP is evident. For this particular simulation, it is interesting to note the existence of a region over Nova Scotia where the deposition of sulphates is significantly greater than that which could be expected from local sources. This is interpreted as being due to the confluence of two flows that pass over two different centres of high emission ofSC>2, andas being evidence of the model's ability to qualitatively model LRTAP.